The long term goal of this proposal is to determine the role of a novel PI- 3 kinase in hematopoietic cell growth. A novel phosphatidylinositol (PI) pathway which is associated with growth factor receptor binding and transforming oncogenes in fibroblasts has recently been described in our laboratory. This pathway is distinct from that which generates the well- characterized second messenger, inositol-1,4,5-P3 from PI-4,5-P2. The first step in the previously characterized PI pathway is phosphorylation of PI on position 4 of the inositol ring. In the new pathway, the first step involves phosphorylation of PI in position 3 of the inositol ring to generate a novel isomer,phosphatidylinositol-3-phosphate (PI-3P). Based on previous studies from our laboratory, we propose that this pathway is involved in transduction of mitogenic signals. The novel pathway of PI metabolism is not restricted to fibroblasts. I propose to characterize this pathway in human and murine hematopoietic cells and determine its role in mediation of cellular responses to CSF-1, a macrophage growth factor, whose receptor has tyrosine kinase activity. The Specific Goals are: a) Role of PI-3 kinase in signal transduction initiated by growth factors in hematopoietic cells. I will investigate the association of PI-3 kinase activity with the biological responses of CSF-1 receptor. b) Development of monoclonal antibodies to PI-3P. Hybridomas secreting antibodies which react with the phospholipids of interest have been generated. These antibodies will be purified and characterized. c) Metabolic fate of PI-3P in cells. I will determine whether PI-3P is hydrolyzed by phospholipases or converted into higher phosphorylated species in response to growth factors. e) Characterization of PI-3 kinase from human hematopoietic cell line, K562. The enzyme will be purified and polyclonal antibodies to PI-3 kinase will be developed to aid in measurement of total cellular PI-3 kinase.